Method of reducing cut-growth rate of rubberlike butadienestyrene copolymer



Patented June 14, 1949 METHOD or REDUCING CUT-GROWTH RATE or RUBBERLIKE BUTADIENE- STYRENE COPOLYMER Arnold R. Davis, Riverside; Conn, assignor to American C'yanamid Company, New York, N. Y., a corporation of Maine NoiDrawing. Application January 29, 1945, Serial N0. 575,191

This invention relates to the vulcanizing of synthetic rubber-like'materials. More particularly, the invention relates to an improved process of vulcanizingsynthetic rubbers. of the butadiene-styrene copolymer type, whereby products of decreased brittleness and exhibiting a remarkably low cut-rate growth are obtained.

In the fabrication of various articles such as tires, footwear and the like from synthetic rubber-like materials; a problem occurs which is not encountered when using natural rubber in a similar manner. This problem is that of the rate at which a small cut will grow as the fabricated rubber-like composition is flexed. In the case of vehicle tires particularly, the problem is further aggravated by the fact that in use the'articles are subjected to the same flexing which inducesthe growth of any cut which may beaccidentally caused. V

It is, therefore, a principal object of the present invention to produce a rubber composition which when fabricated and/or vulcanized will be subject to a minimum of difiiculty with out growth. At the same time; it is a further object of the invention to obtain rubber-like compositions which in addition to a low out growth rate, are less subject to brittleness after vulcanization than is true of currently-available materials of similar types.

In general, the accomplishmentof the desired objects of the present invention are, obtained by incorporating in the rubber-like composition a small amount oilime, magnesia or salts thereof with weak acids. It has been found that the addition of very small amounts of these materials, amounting to from about 0.1 to 0.5% by weight of the butadiene styrenecopolymer in the composition, the .rate at which a cut increases in length or depth as the vulcanized composition is flexed may be reduced from a third to a half.

The practice of the present invention is relatively simple, having the advantage that no alterations in the usual procedures of compounding, fabricating and vulcanization need be made.

' The usual fillersfstrngth'enersj softening agents and organic accelerators are used. There is no required alteration in the time temperature cycle during vulcanization. The only change required is the simple addition of the calcium or magnesium'containingmaterials. These are added very simply as an additional compounding in- 3 Claims. (01. zoo-41.5)

' other compounded ingredients.

materials.

gredient in the normal preparation of n the In this respect. it should be noted that the present invention is not related in anyway to the very old practice of accelerating thevulcanization of rubber by adding; in addition to sulfur, avery large quantity such as'10 to 15% 'ormore of magnesia or the like, where the MgO is usedas an auxiliary accelerator in ratios of 1:2 or more with other accelerators. In such a case, the magnesia is present as an accelerator per se and is required 'in'large amounts; so large in many casesas to be a very appreciable item when compared with the Further, such materials in such large amounts are undesirable because of their efiect 'on'the hysteresis properties. i a .7 r Y.

In the present case; the acceleration is'provided by the usual organic'acceleratorssuch as mercaptobenzothiazole, its derivatives and other analogous products which are common and well knownin the art. The lime and magnesium compoundsare added in what are in effect catalytic amounts. The exact reason for their efiect on the brittleness and cut-rate growth of the finished product is not known. As' little as about 0.1% by weight of the rubber-like copolymer produces a beneficial efiect. --More.than about 0.5 to 0.6% produces no appreciable additional improvement andis therefore not required. This amount is small enough so that considerations of hysteresis are negligible. I

The invention will be described in greater particularity in conjunction with the following examples which are intended to be illustrative only and not by way of limitation. All parts are by weight unless otherwise noted. Where aging of the samples is referred to, a'48 hour storage 1 treatment in an oven at 100 C. is indicated un 0 less otherwise specified.

Ex t Irma 1 a cept that compound B contains an additional ingredient amounting to 0.15 pound of light-calcined magnesia. As shown in Table I, thissmall amount of material has-no adverse efiect onthe setup'tests as determined by the Y value on a 3 '4 Williams plastometer. The hardness of the ma- The following table (Table II) shows that terial is somewhat better after being cured than the sample containing the 0.15 part of light-calwhen the magnesia is not present and the torcined magnesia per 100 parts of butadiene-stysional hysteresis is not appreciably altered. Howrene copolymer produces vulcanizates which ever, the cut-rate growth on both the aged and r have higher elongation both before and after unaged samples has been decreased more than aging.

Table H Mod. at Mod. at Tensile 1 Elong., Set, Cure 200% 300% Strength Per cent Per cent O 30 t i g id i 350 700 2 860 Compound nw 265 515 2: 550 Compound A}A ed 1,025 2, 700 Compound B g 775 2, 625 60 min. at 141 0.:

tsszzsih l 233 232 $1388 Compound A}A ed 1,060 2, 750 90 Qomlgggilgl 1 3 g s40 2,685

azsssrss 2?; e; Compound A A ed 1, 000 2,750 Compound B g s 2, 91a

' 1 Modulus and Tensile in pounds/sq. in.

1 Set at break 2 min. after break.

%. In Table I and the succeeding tables, the EXAMPLE 2 following symbols are used to represent thevari- Similar compositions were prepared to those ous indicated accelerators: in Exam ple l, but using 0.5 part per 100 of hy- MBTJmercaptobenzothmzole drated lime. The formulations and physical oMBTzbenzothiazyl dismfide r0 erties are shown in Table IIIand the tensile DOTG=diorthot01ylguanidine g gz tests in Table W.

AAC=a blend of mercaptobenzothiazole and the adduct of diphenyl 'guanidine-zinc chloride. Table III Table I Compounds Compounds 0 D Per Cent Change s @1350 1 er rs.in oi' g z .1 7

Per cent Change +21 +21 SHORE HARDNESS Minsiates Cure at 141 0.:

SHORE HARDNESS 50 58 53 -62 56 (0 5-30 5D dwell) Minutes Cure at 141 0.: OUT GROWTH RATE it; 33:: 5-5 3:55 MUS/1510617018 60 minute Cure Before Aging. 30 20 TORSIONAL HYSTERESIS After 24 hrs. at 100 C 72 38 K" at 280 F. TEAR RESISTANCE 60 minute Cure, after 48 hrs. at. 100 C 103 142 CUT GROWTH BATE TORSIONAL HYSTERESIS Mi1s/1000 flexes "K" at 280 F.

60 minute cure, unaged 17 12 Aged 24 hrs. at 100 C 35 25 60 minute Cure, Unaged .135 .180

Table IV Mod. 1 at Mod. 1 at Elong. 200% 300% Fran Per Cent mn. at 1413(2); 24 85, 8

ompoun 0 4 1, 70 590 CompoundD Unaged 205 355 1, 540 740 Compound C} ed 1, 095 2, 585 370 CompoundD g 210 I 2,500 415 60 :1% 5 1 030 2 s00 0 ompoun 50 65 Compound D} 390 's00 2, 510 010 Compound C} ed 1,400 2,560 1 305 CompoundD g 1,050 2,550 380 90 :1% 03 1 205 2 880 50 ompoun o 5 Compound 1)} 420 570 2, 075 585 Compound C} ed 1,330 2,710 325 CompoundD g 1,010 1,815 410 1 Modulus and Tensile in 1bs./sq. in.

EXAMPLE 3 SHORE HARDNESS Example 2 was repeated using 0.5 part per 100 Cmpmmds of magnesia and using severaldifierent organic E G accelerators. The formulation and physical Properties are shown in the following Tables Min gates Cure at 141 0.: 50+ 48 V and VI. 25 00+ 55- 50 51 55+ 51- 50 Table V 120 61+ 50 61 55+ CUT GROWTH RATE 0 1 0 30 milslk ilocy ole I .E. F G H M1uute Cure, Unaged 28 21 v 27 H Aged 24 hrs. at 47 50 03 I -40 g n s n 100 v 100 100 12 80 Coal Tar Softener .0 35 Per Cent Rebound xide .3 111' Liglt calcined magnesia 5 60 Minute Cure at 141 C 38 38 38 39 h TORSIONAL HYSTERESIS Set-up Tests .h v

I 1110 es 5 1 No Heat .155 .155 .155 .157 40 K at After 2.5 hrs. in Boiling H 0".-. v.180 201 .20 .218 I Per Cent Change +20 +296 +303 00 Minute Cure at 141 0 .107 .220 .102 .197

Table VI our Mod. at Mod. at Tensile E1ong., e 200% 300 Strength percent 30 min. at 141 C.: Compound E +240 +455 +1930 745 Compound F Unaged 255 1005 780 Compound G 210 455 1780 735 Compound H 1565 750 Compound E 2, 450 3 70 V gggp F Aged 37 530 pound G 340 320 Compound H 2, 130 320 60 min. at 141 0.:

01111 Compound G Unaged 2,875 580 Compound H 2. 630 640 Compound E 2, 530 300 gompound F Agedfln. 2,695 465 ompound G 2, 255 265 CompoundH 2,230 290 90 min. at 141 C.:

01111101111 1 3 Compound G Umged 2, 005 470 Compound H 2, 420 535 Compound E 2, 300 285 gompound F Aged 2,610 425 ompound G 2, 460 Compound H 2, 435 min. at 141 0.:

8 55 om oun 0015805115 G l 2,770 Compound H 2, 920 Compound E 2, 540 Compound F Aged 2,770 Compound G 2,415 Compound H 2, 350

1 Modulus and Tensile inlbsJsqL in.

acids such as oleic acid, linoleic acid, stearic acid a and the like and naphthenic acids. They have also been employed in the form of their zinc salts. and less commonly as their copper salts. In accordance with the present invention, it has been found that if these materials are used as their calcium or magnesium derivatives the benefic'ial effect of the latter is also obtained, not only.

on the cut-rate growth but on the brittleness and tensile strength which is particularly evident after aging.

EXAMPLE 4 Use of these calcium and magnesium salts of several weak acids is listed in the following Table VII, showing various formations and physical properties-resulting therefrom, a standard using stearic acidper se is also shown.

Table VII Compounds I J K -S 100 100 100 50 50 50 5 5 5 2 2 2 8 8 8 O. 495 '0. 495 0. 495 0. 705 0. 705 0. 705 Stearic Acid l. 8 Calcium Stearate 2 Magnesium Naphthenatc 2 OUT RATE GROWTH MilsllOOO Flexes Minutes Cure at 141 0.: Unaged,-60 13 10 Aged 24 hrs. at 100C 60 33 26 22 60 Minute Cure at 141 0.:

Unaged-Mudulus at 200% 525 375 325 Unaged-Tensile Strength,lbs [so in 3,475 3,200 3, 300 Unaged-Elongation, percent. 650 700 7 Aged-Modulus at 200% 1,125 900 875 Aged-Tensile Strength, lbs/sq. rn 2, 925 2, 975 2, 825. AgedElongation, percent 410 480 480 EXAMPLE 5 Example: 4 was repeated substituting rosin which had been treated with calcium and magnesia hydroxidefor the calcium and magnesium salts of fatty acids. The formulation and physical I claim:

1. A method of reducing the out-growth rate of flexible, vulcanized, rubber-like butadienestyrene copolymer compositions obtained by vulcanizing a composition comprising an unvulcanized, vulcanizable, rubber-like butadienestyrene copolymer, sulfur, an organic accelerator and zinc oxide in amount sufficient to fully activate the organic'accelerator; which method comprises forming a. composition of said unvulcanized, vulcanizable butadiene-styrene c'opolymer, sulfur, organic accelerator, and zinc oxide, adding theretofrom 0.1-0.6% by weight of the polymer of a substanceselected from the group consisting. of the oxides. of calcium and. magnesium mechanically working said composition until the components thereof are substantially uniformly disseminated. therein, and then subjecting the composition to vulcanization.

2. A composition vulcanizable to a flexible vulcanizate characterized by a low cut-growth rate, which composition comprises an unvulcanized, vulcanizable rubberelike butadiene-styrene copolymer, sulfur, an organic vulcanization accelerator, zinc oxide, said zinc oxide being present-in amount sufficient, to fully activate said organic accelerator, and from (Ll-0.6% by weight of the polymer of ansubstance selected from. the group consistingofrtheoxides.of calcium and magnesium.

3. A flexible vulcanizate prepared by vulcanizing axcompositioncomprising an unvulcanized, vulcanizable rubber-like butadiene-styrene copolymer, sulfur, an organic vulcanization accelerator, zinc oxide, said zinc oxide being present in amount sufficient to fully activate said organic accelerator, and from (ll-0.6% by weight of the polymer of a substance selected from the group consisting of the oxides of calcium and magnesium, said vulcanizate being characterized by a-low cut-growth rate and in having tortional hysteresis characteristics differing inappreciably from the tortional hysteresis characteristics of a similar vulcanizate from which the oxides of calcium and magnesium are omitted.

ARNOLD R. DAVIS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS properties are shown in Table VIII.

Table VIII Compounds L M N. o

CIR-S 100 100 100 EPC Black 50 50 5O 50 Zinc Oxide. 5 5 5 5 Sulfur 2 2 2 2 Softener (Petroleum Hydrocarhon) 10 7 7 7 F. F. Wood Rosin 3 Limed Wood Rosin (4.

OH -1 3 'WoodO Rosin' Containing (5% 3 6. 1%? "61595 "of 465' 0.495

0. 705 0. 705 0. 705 0. 705 Williams 3 min. Y at 100 C; v inches N0 Heat. 117 117 118 117 After 2.5 hrs. in Boiling H 0... .142 131 131 .130

Per Cent Change +21 +12 +11 +11 Pages 9, 41 and 43, The Compounding oi Buna S,'Report No. 42-4 Dec. 1942, published by E. I. du. Pont de Nemours 8: Co., Wilmington, Del. (Copy in Div. 50.) 

